Electrodes for electrostatic apparatus



April 12, 1955 C. C. COOK, JR

ELECTRODES FOR ELECTROSTATIC APPARATUS Filed Sept. 1, 1953 IN VEN TOR ATTORNEY United States Patent '0 ELECTRODES FOR ELECTROSTATIC APPARATUS Charles C. Cook, Jr., Lakeland, Fla., assignor to International Minerals & Chemical Corporation, a corporation of New York Application September 1, 1953, Serial No. 377,767

3 Claims. (Cl. 209-127) This invention relates to the art of electrostatic separation of ore components and, more particularly, to apparatus by means of which such electrostatic separations may be effected. More particularly, the invention relates to that field of the art of electrostatic separation which utilizes the phenomenon of contact potential as a means of differentially charging ore particles prior to the electrostatic separation thereof wherein the charged particles are subjected to the action of an electrostatic field when in a freely falling state.

Various forms of apparatus in this general field have been designed and are described in the literature. The patent to OBrien No. 2,168,681 shows several forms of apparatus by means of which particles of ore'may be separated by subjecting them as freely falling bodies to the action of an electrostatic field. Although the particular method of differentially charging the ore particles is unimportant, insofar as the present invention is concerned, it is to be observed that charging of the particles may be effected either by contact thereof with a source of free electrons as, for example, by contact with a grounded plate of suitable material, or the differential charge may be accomplished by intimate contact of the particles over a substantial area and then separation thereof under conditions where surface conductivity will not dissipate the charge. In any event, it is understood that the previously comminuted ore will have been subjected to such an action that the various components thereof will be sufficiently differentially charged to render them responsive to the action of an electrostatic field whereby relative lateral displacement of the respective components will take place to enable an effective separation to be accomplished.

As will be seen from the above patent to OBrien, the electrodes that are utilized are in the form of flat plates suitably spaced and connected in suitable electric circuits in order that a desired field gradient of potential may be maintained during the separation operation.

It has been found, under certain conditions of operation, that effective separation is hindered by reason of the fact that particles of ore will contact one of the plates and have its charge reversed, whereupon the particles will be attracted in the opposite direction and thus contaminate the fractions derived at the bottom of the mechanism where the collection takes place. It also happens, on occasion, that particles will adhere to the flat electrode surface and, upon continued accumulation, will impair the character of the operation.

In order to overcome the ditficulties above mentioned that are sometimes experienced in the use of fiat plate electrodes, various forms of electrode structures have been designed by means of which the freely falling particles may be caused to move past the primary electrode faces and into zones where they will not contaminate the fractions of the ore that are properly separated and collected during the beneficiating process.

An object of this invention, accordingly, is to provide an electrostatic apparatus in which ore particles are subjected to an electrostatic field while falling freely through the field but wherein the accumulation of such particles upon the faces of the electrodes is avoided or substantially reduced.

Yet another object of the invention is to provide an apparatus of the above character wherein the impairment of separation due to contact of the particles with the electrode face and the occasioning of a reversal of charge thereof may be avoided.

2,706,044 Patented Apr. 12, 1955 Yet another object of the invention is to provide apparatus of the above character wherein an electrostatic field of relatively high field gradient may be maintained during a predetermined initial desired fall of the particles and, following such initial fall, subjecting the particles to a somewhat reduced field gradient but under conditions such that greater room will be provided for movement of the particles in response to the field.

The foregoing and other objects are attained by providing banks of spaced electrode elements to provide the desired interstitial spaces and forming the lower portions of the elements with a curvature such that the elements of the opposed electrodes diverge gradually away from the separating zone.

In order that the invention may be understood more fully, it will now be described with reference to the accompanying drawings wherein:

Fig. l is a view in end elevation, partly in section, showing an electrostatic separating apparatus constructed in accordance with the present invention;

Fig. 2 is a view in side elevation showing the apparatus of Fig. l; and

Fig. 3 is a view in horizontal section, taken on the plane indicated by the line 3-3 of Fig. 2, looking in the direction of the arrows.

Referring to the above drawings, a feed hopper is illustrated at 10 and may be of any suitable form. It is important, of course, that the structure of the hopper be such as to feed a desired quantity of comminuted ore to be beneficiated uniformly to an electrostatic field indicated generally at 11. The structure of the feed hopper forms no part of this invention and therefore requires no further discussion.

The electrostatic field 11 is formed between banks of tubular electrodes 12 and 13, the banks being connected in a suitable electrical circuit indicated at 14 in order that a desired potential may be applied, through the electrodes, to the electrostatic field 11.

Beneath the electrodes 12 and 13, there are provided a plurality of collection hoppers 15, the structure of which forms no part of this invention. In accordance with well-known practice, the hoppers may be provided with adustable vanes 16 to permit any desired cut to be taken during the operation of the mechanism.

As will be seen in Figs. 2 and 3, each bank of electrodes 12 and 13 consists of a plurality of tubes 17 that are shown as being circular in cross-section and the ends of which are formed with rounded caps 18 in order that no edges may be provided and thus to eliminate, as far i as possible, all corona discharge. The respective banks of tubes 17 are secured in position by means of a header 19 and rounded tubular connectors 20, and the banks 12 and 13 are suitably spaced to provide sufiicient room for lateral movement of the particles in response to the electrostatic field. The voltage gradient of the field is, of course, properly related to the electrode spacing in order to provide this desired gradient, and the spacing of the electrodes depends upon the nature of the material being beneficiated as well as upon the vertical length of the field and the voltage gradient.

In one form of apparatus providing successful commercial separation of potash and phosphate ores, the

electrodes are 6 feet long and are spaced 10 inches apart. A voltage of 90,000 volts is impressed across the electrodes, thus providing an electrostatic field potential gradient of 9,000 volts per inch.

At a point approaching the bottoms of the electrodes, the tubes 17 are bent downwardly and outwardly as illustrated in Fig. l to provide an electrostatic field segment indicated at 21. The point at which the curvature begins may vary somewhat depending upon the material to be beneficiated, the voltage gradient, and the optimum length and spacing of the tubular electrode elements. In one form of apparatus that has produced satisfactory commercial separations of phosphate and potash ores, the curvature of the lower ends of the electrode elements of tubularform begins at about 4 feet and continues on a radius of about 10 feet. The field segment or zone 21 thus formed provides more room for the particles to spread during their lateral displacement as freely falling bodies through the electrostatic field. While thus continuing to spread, they are still subjected to electrostatic forces similar in nature to those of the forces in the upper portion of the field 11 although somewhat diminished in intensity as the electrode faces diverge.

As hereinabove stated, a marked advantage has been discovered in the use of the tubular electrode element structure over the use of flat plates, especially during rougher separations of the ore. Where quartz is present in large quantities, the advantage of the tubular structure is increased because, with such structure, there is a reduced tendency of the highly charged quartz particles adhering to the electrodes and having a reversal of charge take place, causing the silica particles to move toward the other electrode and thus impair the separation. Also, as above-mentioned, the tubular and diverging form of electrode elements prevents the accumulation of ore particles upon the outer faces of the electrodes and thus prevents the impairment of the field gradient during operation. It has been found that the motion of the particles laterally and toward the respective electrodes tends to cause these particles to move beyond the outer faces of the electrodes and, if there is a tendency to adhere, they will adhere to the rear faces where certain accumulations may take place without impairing the nature of the electrostatic separation.

Having thus fully described and illustrated the character of the invention, what is desired to be secured and claimed by Letters Patent is:

1. Electrostatic separation mechanism comprising means for feeding pulverulent material, spaced electrode means beneath the feeding means, each of the electrode means comprising a plurality of tubular elements, means to mount the elements of the respective elec trode means in spaced vertically extending relation to form an electrostatic field, the lower portions of each of the elements of each of the respective electrode means diverging outwardly and downwardly to provide a zone of. greater width than the field formed by the electrode portions above the lower portions, and means beneath the electrodes to collect pulverulent material passing therebetween.

2. Apparatus according to claim 1 wherein the tubular elements are of circular cross section.

3. Apparatus according to claim 1 wherein the lower portions of each of the elements curve downwardly and outwardly.

References Cited in the file of this patent UNITED STATES PATENTS 2,168,681 OBrien Aug. 8, 1939 

1. ELECTROSTATIC SEPARATION MECHANISM COMPRISING MEANS FOR FEEDING PULVERULENT MATERIAL, SPACED ELECTRODE MEANS BENEATH THE FEEDING MEANS, EACH OF THE ELECTRODE MEANS COMPRISING A PLURALITY OF TUBULAR ELEMENTS, MEANS TO MOUNT THE ELEMENTS OF THE RESPECTIVE ELECTRODE MEANS IN SPACED VERTICALLY EXTENDING RELATION TO FORM AN ELECTROSTATIC FIELD, THE LOWER PORTIONS OF EACH OF THE ELEMENTS OF EACH OF THE RESPECTIVE ELECTRODE MEANS DIYERGING OUTWARDLY AND DOWNWARDLY TO PROVIDE A ZONE OF GREATER WIDTH THAN THE FIELD FORMED BY THE ELECTRODE PORTIONS ABOVE THE LOWER PORTIONS, AND MEANS BENEATH THE ELECTRODES TO COLLECT PULVERULENT MATERIAL PASSING THEREBETWEEN. 